1. Field of the Invention
The present invention relates to a zoom lens system suitable for a video camera and an electronic still camera using a solid-state imaging device and the like.
2. Related Background Art
A zoom lens system in which an optical-path-folding optics is included suitable for a solid-state imaging device has been proposed in Japanese Patent Application Laid-Open Nos. 8-248318, 2000-187160, 2002-341244, and 2004-069808.
However, in a zoom lens system disclosed in Japanese Patent Application Laid-Open No. 8-248318, since the first lens group is composed of lens elements having positive refractive power, the first lens group tends to become large.
Moreover, in a zoom lens system disclosed in Japanese Patent Application Laid-Open No. 2000-187160, in order to miniaturize the dimension of an optical-path-folding optics, the folding optics is disposed nearly at the center of the optical system. Accordingly, a plurality of lens elements are disposed to the object side of the folding optics, so that it becomes difficult to miniaturize the whole optical system.
Moreover, in a zoom lens system disclosed in Japanese Patent Application Laid-Open No. 2002-341244, in order to miniaturize the optical system, the first lens group is composed of lens elements having negative refractive power. However, since focusing is carried out by the third lens group having positive refractive power, the moving amount of the lens group becomes large upon focusing on a closest object, so that it becomes necessary to secure a large space. Accordingly, it becomes difficult to miniaturize the whole optical system.
Furthermore, in a zoom lens system disclosed in Japanese Patent Application Laid-Open No. 2004-069808, in order to miniaturize the optical system, since the position of the aperture stop is fixed upon zooming, the total lens length of the optical system becomes large. As a result, the height and the dimension of the camera becomes excessively large.